Indeterminate growth, the life-long growth without fixed limits, is
typical of some evolutionarily very successful aquatic
invertebrate groups such as the decapod crustaceans, bivalve
molluscs and echinoderms. These animals enlarge their organs
also in the adult life period and can regenerate lost
appendages and organs, which is in sharp contrast to mammals and most
insects. Interestingly, decapods, bivalves and echinoderms
develop only rarely neoplastic and age-related diseases, although
some species reach ages exceeding 100 years. Their stem cell
systems must have co-evolved with these successful life histories
suggesting possession of unknown and beneficial features
that might open up new vistas in stem cell biology. Research of the
last decade has identified several adult stem cell systems
in these groups and also some mature cell types that are capable
to dedifferentiate into multipotent progenitor cells.
Investigation of stem and progenitor cells in indeterminately growing
bilaterian invertebrates is assumed beneficial for basic
stem cell biology, aquaculture, biotechnology and perhaps medicine.
The biggest treasure that could be recovered in these animal
taxa concerns maintenance of stem cell niches and fidelity of
stem cell division for decades without undesirable side
effects such as tumour formation. Uncovering of the underlying molecular
and regulatory mechanisms might evoke new ideas for the
development of anti-ageing and anti-cancer interventions in humans.

Kyle McLea’s Marmorkrebs project made it total long ago. Indeed, it’s been this round’s “break-out project” in terms of percent raised compared to target - more than 200%.

But I want to talk a bit about the overall amount we’ve raised at #SciFund. We cracked the $90,000 mark yesterday.

I cannot tell you how fantastic it would be to hit the $100,000 mark. So please, check out the projects to see if there are any that would like to support, even with a dollar or two. (Moral support matters a lot!)

Importantly, as a crustacean biologist, I can also see how they’d be useful models for other, larger, more “economically important” decapod crustaceans like lobsters and crabs, for which rearing is very difficult or impossible with current techniques. Although Marmorkrebs have a fairly long generation time and only a “primitive” crustacean has had its genome sequenced, marbled crayfish are easily kept and reared and have a number of other reasons in their favor as a useful model organism.

Now, I don’t want to tread where others have already walked. Important in the “What can we use the Marmorkrebs to study?” literature is Günter Vogt’s 2008 article in the Journal of Zoology.

Vogt discusses many reasons why Marmorkrebs are of use to a scientist—they are easily grown and cared for, they “breed” all year round, all life stages are accessible for examination, and more. They have large eggs found outside the body that are excellent for those studying development from the embryonic stage to adulthood.

He goes on to make the case that marbled crayfish will be useful for developmental biology, stem cell research, and studies of regeneration. In addition, because the animals are genetically identical, epigenetics and epigenomics may be a powerful niche where these clone crayfish can prove their utility. Epigenetics is the study of variation that is not dependent on the DNA sequence of an organism—and in epigenetics we see marks of diet, aging, and other happenstances of life stamped “upon” the DNA but not actually changing its sequence. The definition of an epigenetic effect is seeing differences in some phenotype (outward appearance of a trait) in an organism among isogenic (genetically-identical) animals. For epigenetics, which will be enormous in 21st century biology, a genetically identical crayfish may be just what we need.

Vogt also goes on to recommend marbled crayfish for studies of evolution and for toxicology studies. I’m going to talk about the latter before moving on to some other reasons to be excited about these incredible crayfish.

Crayfish have long been lauded as “sentinel species” for monitoring environmental quality. A number of parameters of crayfish physiology are helpful to scientists studying pollution, including how these animals survive, what metals or contaminants they accumulate in their tissues, and more. So, Marmorkrebs can certainly serve just as well as other crayfish. But in fact, their genetic identity is of further use in toxicology studies. Smaller numbers of animals in a given strain are needed for testing if they are all genetically identical and react similarly to a drug or toxin. And although it seems counter-intuitive, testing a few different strains or lines within a species may demonstrate greater total genetic variance than looking at a single outbred strain of animals in greater numbers. So in the end, we can maintain large numbers of the small marbled crayfish for toxicology studies, minutely manipulate their environment by introducing drugs or environmental chemicals, and perhaps get a better read out on toxicities and safety than we might even get from rodents. Now, I think a lot more studies are really needed before we could actually demonstrate that, but it is a potential use. And these animals would surely be better models for toxicology of invertebrates regardless.

Finally, I also think these clone crayfish will make a great model organism for genetic studies. We don’t have many macroscopic (visible without microscopy), multicellular organisms that are both isogenic and easily genetically manipulable. (That is, can we introduce new genes? Can we change the ones that are there?) Marmorkrebs could fill that need.

Which brings me to the ultimate point of this entire article, for those who are still reading. I have a project that is a small step in the study of marbled crayfish and their genetics.

In collaboration with Doctor Zen, I’m raising money (through the #SciFund Challenge) to study the genes of Marmorkrebs and get a lot more information about their organization and the similarity between lines descended from different crayfish mothers. How genetically identical are they? What differences do we see between lines? How about if we compare them with the sexual version of Marmorkrebs, Procambarus fallax? (Which I haven’t mentioned, but is another whole neat aspect of the Marmorkrebs story!) There is so much to learn.

But if you’ve read this far and are interested to help us learn more, consider funding this project with a $1 or $5 donation here. Or if you can’t donate, consider spreading the word to your friends and social networks.

Thanks, and remember: Never send a sibling (or some outbred critter) to do a clone’s job. That’s what we have Marmorkrebs for.

BioInvasions Records is an open access, peer-reviewed international journal focusing on applied research on alien species and biological invasions in aquatic and terrestrial ecosystems of Europe, North America and other regions. The journal provides the opportunity of timely publication of first records of aquatic and terrestrial invaders and other relevant information needed for risk assessments and early warning systems. Also, relevant technical reports and conference proceedings can be considered for publication in this journal.

We welcome submissions to the journal and of course encourage you to use it as a resource.

To be honest, I hope this journal never gets a Marmorkrebs paper, because that would mean another introduction of Marmorkrebs. Indeed, this is one journal that I wish would fail... but only because there were no biological invasions to report.

Phosphatized globular microfossils from the Ediacaran and lower Cambrian of South China represent an impressive record of early animal evolution and development. However, their phylogenetic affinity is strongly debated. Understanding key processes and conditions that cause exceptional egg and embryo preservation and fossilization are crucial for a reliable interpretation of their phylogenetic position. We conducted phosphatization experiments on eggs of the marbled crayfish Procambarus that indicate a close link between early mineralization and rapid anaerobic decay of the endochorional envelope. Our experiments replicated the different preservational stages of degradation observed in the fossil record. Stabilization of the spherical morphology was achieved by pre-heating of the eggs. Complete surface mineralization occurred under reduced conditions within one to two weeks, with fine-grained brushite (CaHPO4·2H2O) and calcite. The mechanisms of decay, preservation of surface structures, and mineral replacement in the experiment were likely similar during fossilization of Cambrian embryos.

Keywords: None provided.

Note: This is the final version of record of a paper that previously appeared as a discussion paper; abstract here.

22 May 2012

Today, a guest post from Kyle McLea, who has been carrying the Marmorkrebs banner for this round of #SciFund.

As a crustacean biologist who has chiefly studied crabs and lobsters, I’ve been fascinated by the marbled crayfish (Marmorkrebs) for years and for a number of reasons that I’ll detail below. But the first thing that attracted me was simply this.

Really? A crayfish that clones itself?

When Doctor Zen asked me to guest blog on the Marmorkrebs blog I was sure I had a lot to say about my interest in these fascinating critters, but I also wanted to speak to the wider interest of the scientific community. In short: Why should scientists (and the public) care?

To which I say: Never send a (mere) sibling to do a clone’s job.

Let me explain.

Marmorkrebs are a parthenogenetic crayfish. All known examples are female and reproduce themselves entirely without sex. This makes it the first example of a decapod crustacean (and there ~15,000 known species of crabs, lobsters, shrimp, and crayfish!) that only reproduces asexually. There have been a couple of other examples of crayfish that have been found to be genetically identical or to sometimes reproduce asexually, but marbled crayfish were the first found to procreate this way exclusively.

So, in a word, we’re dealing with clone crayfish.

To anyone who’s been following the molecular biology revolution over the past 30ish years, the word clone has both amazing power and amazing misuse and confusion. Clone can mean a lot of things. In this case, I’m not talking about cloning genes (experimentally extracting pieces of nucleic acid, sequencing them, and using them to assemble recombinant—new—combinations of DNA sequence for introduction to a different organism) or about using somatic-cell nuclear transfer to clone embryos (like Dolly the sheep). What I’m saying is that mother and daughter marbled crayfish should be genetically identical, or nearly so, much like identical twins in humans.

It turns out that scientists have thought a lot about the benefits of studying genetically identical individuals in a population, pretty much for as long as there has been a science of genetics. Case in point for inbred (nearly genetically identical) organisms:

“Just as the purity of the chemical assures the pharmacist of the proper filling of the doctor’s prescription, so the purity of the mouse stock can assure a research scientist of a true and sure experiment...In experimental medicine today... the use of in-bred genetic material... is just as necessary as the use of aseptic and anti-septic precautions in surgery.” —C.C. Little, 1936

Now Little may have held some ill-conceived notions about eugenics and the role of tobacco in causing cancer, but on the importance of genetically-identical (isogenic) and inbred laboratory strains he was a pioneer. His work to build up the Jackson Laboratory in Bar Harbor, Maine (the mecca of 5000 unique strains of mice), was a key part of the rise of defined strains and breeds of laboratory animals that continues today.

Those laboratory strains serve as “models” for various human diseases and for particular functions of human physiology, such as immunity or heart function. Among the model organisms listed at NIH, for instance, everything from yeast to mouse and Daphnia to zebrafish can help us to learn about different aspects of human biology and beyond.

But in each case the normal biological variation within an organism confounds us and complicates our study. Unless we want to see the full extent of biological variance (and sometimes we do—safety and efficacy testing of drugs on different populations, anyone?), having organisms that are as close to identical as possible is (often) the goal.

For mice and rats, you might have to backcross (do parent/offspring matings) for more than 20 generations to have a sufficiently inbred line to call it “genetically identical” (and I suspect some gene variation may still exist). Now, mice breed fast, but 20 generations is still real time (years) in the life of a scientist. In the mean time, scientists resort to use of siblings, littermates, or much less inbred animals. These animals have many more differences at the genetic level.

I know you’re seeing where I’m going with this… if an organism started out genetically identical, you’d have a great edge in using this organism to study any number of interesting things. Bringing us back to Marmorkrebs.

Lines of the marbled crayfish are believed to be genetically identical because they do not participate in the normal exchange and shuffling process that accompanies sexual reproduction. But of course, mutations happen to us all. So they’re not likely to be absolutely 100% identical between individuals, but much closer than anything else in the world except for natural identical twins/triplets/etc.

So, I say, send in the clone crayfish. With these animals, we don’t need to compare results with a genetically-different sibling or with an unrelated animal. This unique animal can not only be a useful biological model, but we also don’t have any easily-reared decapod crustacean that can really compete with marbled crayfish, if you take into account their genetic identity.

While they might not be a great model organism for general human physiology (they are crustaceans, after all), there are some specific ways they can help us understand human physiology (e.g., nerves) and they have a lot of other potential uses as a model organism.

15 May 2012

The question of what to call Marmorkrebs in the scientific literature has bubbled up again. When I started the blog, there was no proper scientific name, and I suggested using the name “Marmorkrebs,” because it was distinctive. I thought the matter was relatively settled, scientifically speaking, when Martin and colleagues proposedProcambarus fallax f. virginalis as a scientific name for Marmorkrebs.

A paper by Johnson and colleagues poses a strange puzzle. For some unknown reason, they coin an entirely new name for Marmorkrebs: Procambarus sp. malgasy. Nobody else has used this terminology, although Jones and colleagues do refer to “Malagasy Procambarus” in their paper on Marmorkrebs in Madagascar. Maybe it was meant to be Procambarus sp. Malgasy, with the “Malgasy” purely as an descriptive adjective. Then someone at the editing or proofing stage changed the formatting to resemble a species name.

Even so, it doesn’t explain why they wouldn’t refer to Marmorkrebs as “P. fallax f. virginalis.” They have clearly read the paper by Martin and colleagues – it’s in the list of references.Plus, the analysis by Johnson and colleagues supports that Marmorkrebs is most closely related to P. fallax.

Freshwater crayfish have been a mainstay in biological experiments as a model species ever since Huxley’s seminal publication The Crayfish. Crayfish have been used in research ranging from vision pigment studies to neural physiology. Non-native species have been introduced on four continents due to their immense economic value. Although crayfish taxonomy is reasonably well resolved at the highest levels, there are many problems at the levels of genus and species. New exploration, technology and methodology have led to the discovery of not only new species but to a phylogenetic complexity that would not have been imagined in Huxley’s era. This complexity is caused by the conservatism of some morphological characters, high intraspecific diversity and convergence. The ambiguity of crayfish taxonomy is particularly evident for species native to South Georgia and North Florida, which are centers of crayfish diversity. Molecular phylogenetic analyses were employed to provide insight into three aspects of crayfish phylogeny. Using partial data from the 16S ribosomal gene, we determined: (a) the evolutionary relationships of a previously unanalyzed species, Procambarus spiculifer, (b) relationships within the genus Procambarus, and (c) the phylogeny of the entire subfamily Cambarinae. The resulting maximum likelihood tree produced phylogenies that were significantly different from the traditional systematic representation of relationships within the subfamily. Specifically, we show that the subfamily Cambarinae should not be divided into three distinct clades according to the genera Procambarus, Cambarus, and Orconectes. While most members of the genus Procambarus cluster within a single monophyletic clade, the genus Orconectes comprises a parayphyletic grouping that appears to also include members of the genus Cambarus.